Electric cable



March 7, 1939. P. vl HUNTER AL.

ELECTRIC CABLE Filed April 9, 1936 2 Sheena-Shaet l H on.

March 7, 1939. P. v, HUNTER Er A ELECTRIC CABLE Filed April 9, 1936 2Sheets-Sheet 2 Patented Mar. 7, 1939 UNITI-:D STATES PATENT 4orner.

ELECTRIC CABLE Philip Vassar Hunter and Leslie Giddens Brazier, London,and Harry Hill, Kent, England, assignors to Callenders Cable andConstruction Company Limited, London, England, \a British companyApplication April 9, 1936, Serial No. '13,474 In Great Britain April 16,1935 6 Claims. (Cl. 174-25) This invention relates to single core cableshavthrough which the surface of the underlying ingaconductor usually,though not necessarily, of brous layer is exposed. It is also necessaryto stranded form and a dielectric comprising a lamapply the tape in sucha way that its edges do inated body of insulation impregnated with aliqnotproject in a radial direction.

uid or semi-liquid material, the layers of the insu- 'I'he inventionwill now be more fully described 5 lation having, when seen in sectionat right angles with frequent reference to the accompanying to theconductor, a smooth non-circular form, drawings which show examples ofsingle core cable such as described in the specification of U. S. havingcores constructed in accordance with the Patent No. 1,906,968.invention. In the drawings ig In accordance with the invention paper orother Figure 1 is a perspective view of a length of 10 soft fibrousmaterial is applied to the outer surcable of which portions of theconstituent parts i face of the conductor to form a smoothing layer havebeen successively removed to expose the of small thickness and over thislayer a smooth structure of the cable.

lapping of'metal tape is applied to form a smooth, Figure 2 is across-section of the cable shown 15 complete, non-circular, elastic,metal surface on in Figure 1 taken on plane at right angles to the 15which the dielectric is subsequently built up in the longitudinal axisof the cable,

usual way. The whole of the cable structure, Figure 3 is a view similarto that of Figure i both inside and outside the layer of metal tape, ofa length of cable having a modiiied form of is then impregnatedfby theusual procedures. core construction,

Under working conditions the metal tape will at Figure 4 is across-section of the cable shown 20 convenient points, such as jointsand terminain Figure 3 taken in a plane at right angles to tions, beelectrically connected with the conducthe longitudinal axis of the cableand tor so that there is no electric eld between the Figure 5 shows ajoint between the conductors two. In general it appears preferable, butnot of adjacent length of cable of the kind shown essential, to use aconductor of non-circular in Figures 1 and 2. 25

cross-section. In both the illustrated examples the conductor Ahelix ofnon-circular cross-section of resilient I is of elliptical crosssectionand oi stranded metal tape may be placed inside the smoothing form. Inthe cable shown in'Figures 1 and 2 the 185781 0f paper 0I Other SOftAbl'OllS material. conductor is directly enclosed in a. soft fibrousThis is lapped on the conductor either directly or layer 2 of smallthickness. This layer is built 3o with an intervening layer of softfibrous material. up of a, suitable number of paper tapes, for in- Ineither case the resilient metal tape is not a stance, tapes of 5 milsthickness, applied helically close lit on the conductor or on the softfibrous in any convenient manner. The radial thickmaterial but there isa small clearance so that ness of the layer will naturally depend tosome ex the tape is free 'to yield inwardly. This resilient tent uponthe sizeand form of the strand. Over 35 tape forms a spring support fora few layers of this foundation layer is applied a metallic covpaper orother soft fibrous material over which ering 3 consisting of two layersof metal tape each the smooth lapping of metal tape is applied. put onhelically with only a small gap between Whether a resilient support isor is not incoradjacent turns and the adjacent layers being so poratedin the fibrous smoothing layer applied to disposed that the gap betweenthe turns in one 4@ the surface of the conductor, the layer is suchlayer coincides with the central region of the tape that it has theeffect of smoothing out the surin the other layer. These tapes aresmooth sur- `face irregularities due to the Wires in the strand facedbronze tapes of 3 mils thickness and about forming the conductoror toother causes so that 200 millimetres width. Naturally tapes of other theouter surface of the layer has a smooth consizes and material may beused providing they 45 tour of regularl form. The metal tape appliedhave a smooth surface and are sufficiently thin over the fibroussmoothing layer thus provides a to be ilexible; for instance, coppertape of about metallic layer having a smooth regular contour 3 milsthickness may be used. Also the metal without undulations correspondingto the posilayer may comprise more than two tapes or it tions of thewires at the surface of the strand. may consist of a single tape only.In the latter 50 The lappings of metal tape forming the non-cirevent, itis desirable to give it a special treatment cular metal surface on whichthe dielectric is to ensure that neither initially nor after bendingbuilt up must be carried out in such a way as to of the cable are thereany projecting edges, such provide a complete covering, that is to say,so as are liable to be produced by applying a metal that there are'noopenings between the turns tape inasingle layer with substantial lap, itbeing understood that overlapping is necessary in order to ensurecomplete enclosure by the layer of the material within it. In order toget the desired smooth surface it is necessary in this case to stretchthat part of the tape which will, when applied, overlap the adjacent.turn. This stretching should of course be proportionate to the increasein periphery produced by the application of a thickness of the tape tothe underlying layer. The stretching is preferably carried out as thetape is being applied in position round the conductor. In all caseshowever the metal, tape should be applied with considerable tension sothat the inner surface is in close contact with the underlying materialand the overlapping parts of the tape or tapes are also in closecontact.

Over the smooth, complete, elastic, metal surface of ellipticalcross-section thus formed is built up the laminated dielectric body 4.of paper tape. 'I'his is enclosed in a-conductive layer 5 which makescontact with the circular lead sheath 6 in the region of the ma'jor axisof the core. 'I'he spaces between the insulated core and the sheath arefilled with gas or, alternatively, they may be' filled partly with gasand partly with impregnating oil or compound and the whole of thefibrous material within the lead sheath is impregnated with insulatingoil or compound by any suitable known process. The sheath 6 is providedwith a protective covering 'I of impregnated fibrous material.Alternativelythe outer part of the cable may be of other form, forinstance, any of the other forms described in the specification of theaforesaid patent.

In the example o f construction shown in Figures 3 and 4, directly overthe strand I of elliptical cross-section is wrapped a tape 9. This is ofbronze and is '7 mils thick and 200 millimetres wide. As is clear fromFigure 4, this tape is not applied so tightly that it lies in contactwith the entire surface ofthe strand I but is so applied h as to leave asmall clearance I0 on each side of the strand so that it may constitutea resilient base for the overlying layers 2 and 3 of paper and metalrespectively. Naturally the resilient tape may be of other suitablemetal and be of any suitable thickness, for instance, from 5-10 milsthick. The smoothing layer 2 of paper consists of three layers of tape,each put on with a small gap between adjacent turns andthe adjacentlayers being so disposed that the gap of one layer is overlapped to asubstantial extent by the tape-of the succeeding layer. It will beappreciated that the thickness of the paper smoothing layer may bereduced owing to the smoothing action of the resilient tape 9.Alternatively, of course, the resilient tape may be applied as an openhelix with a gap up to about 50% of the width of the tape. In this casethe number of. layers of paper or other fibrous material then applied isincreased to ensure a thickness sum"- cient to bridge the gap andprovide a smoothlthe surrounding part of the cable shown in Figures 3and 4 is similar to that of the cable shown in Figures 1 and 2 and willnot be further described.

:Figure 5 shows a method of effecting a conductor joint and of unitingthe metallic smoothing tapes tothe conductor. 'I'he ends of adjacentlengths of cable are prepared by cutting back priate distances. Themetallic tapes forming the surface 3 are then uncoiled and temporarilybent back. 'I'he underlying layer 2 of paper is then cut back to exposethe conductor, the wires of the outer layer of which are cut back also.The ends of the inner part of the two conductors are jointed by the aidof a ferrule I2 and soldering. The tapes 3 are then wrapped over thesolderedjoint and secured to the conductor and ferrule by solderingmetal I3. It will be observed that the outer shape and dimensions of theferrule approximate to the inside of the layer 3 of metal tape so thatthere is no step or break in the contour of the conductor through thejoint. If it is desired to obtain this advantage without cutting backthe outer Wires of the conductor, the thickness of the layer 2 of papermay be increased and/or the thickness of the ferrule I2 may be reducedtomake the thickness of the layer 2 and that of the ferrule correspond.

It has been found, other things being equal, that the improvedconstruction gives the wall of dielectric an increase in effectivestrength of about 50% as compared with a wall of similar thicknessapplied directly to the stranded conductor.

It is believed that this improvement is due, not only to the smoothingout of the contour of the inner conductive surface to which the wholedielectric is applied, but also to the fact that the conductor, asmoothing layer of small thickness surrounding said conductor andconsisting of soft fibrous material, a complete, elastic, smoothsurfaced, metal layer of non-circular cross-section enclosing saidsmoothing layer and consisting of at least one helical lapping of metaltape, impregnatng iluid in the interstices in the structure enclosedby'sai'd metal layer, an impregnated laminated body of insulation builtup on said metal layerand an impervious sheath surrounding saidlaminated body of insulation.

2. A singie core electric cable comprising a ccnductor, a smoothinglayerof small thickness surrounding said conductor and consisting ofsoft fibrous material, a spring supp^rt of n'ncircular cross-sectiondisposed inside said smoothing layer, a complete, elastic,smooth-surfaced, metal layer of non-circular cross-section enclsing saidsmoothing layer and consisting of at least one helical lapping of metaltape, impregnating fluid in the interstices in the structure enclosed bysad metal layer, an. impregnated laminated body of insulation built upon said metal layer and an impervious sheath surrounding said laminatedbody of insulation.

3. A single core electric cable comprising a conductor, a helix ofnon-circular cross-section of resilient metal tape directly surroundingsaid conductor with a small clearance between it and the conductor, asmoothing layer of 'small thickness surrounding said helix andconsisting of soft fibrous material, a complete, elastic,smoothsurfaced, metal layer of non-circular cross-section enclosing saidsmoothing layer and consisting of at least one helical lapping of metaltape impregnating fluid in the interstices in the structure enclosed bysaid metal layer, animpregnated laminated body of insulation built up onsaid metal layer, and an imprevious sheath surrounding said laminatedbody of insulation.

4. An electric cable system comprising a single conductor, a smoothinglayer of small thickness surrounding said conductor and consisting ofsoft brous material, a complete, elastic, smoothsurfaced metal layer ofnon-circular cross-section enclosing said smoothing layer and consistingof at least one helical lapping of metal tape, said layer beingelectrically connected to said conductor at intervals, impregnatingfluid in the interstices in the structure enclosed by said metal layer,an impregnated laminated body of insulation built up on said metallayer, and an impervious sheath Surrounding saidlaminated body ofinsulation.

5. A single core electric cable comprising a conductor, a smoothinglayer of small thickness surrounding said conductor and consisting ofsoft brous material, impregnating fluid in the interstl'ces in saidconductor and in said smoothing layer, a smooth walled, elastic, metaltube of noncircular cross-section which consists of at least one helicallapping of metal tape and which encloses said conductor and saidsmoothing layer and is responsive to variations in the volume of saidimpregnating fluid, an impregnated laminated body of insulation built upof said tube, and an impervious sheath surrounding said laminated bodyof insulation. f

6. A single core electric cable comprising a conductor, a smoothinglayer of small thickness surrounding said conductor and consisting ofsoft ibrous material, a complete, elastic, smooth surfaced, metal layeroi eliptical cross-section enclosing said smoothing layer and consistingof at least one helical lapping of metal tape, impregnalting liuid inthe nterstices enclosed by said metal layer, an impregnated laminatedbody of insulation built up on said metal layer, and

an impervious sheath surrounding said laminated body of insulation.

PHILIP VASSAR HUNTER. LESLIE GIDDENS BRAZIER. HARRY HILL.

